﻿<p>The projection element is a specialization of the general feature element to represent projections applied to building elements. It represents a solid
attached to any element that has physical manifestation.</p>

<blockquote class="example">
EXAMPLE&nbsp; A wall projection such as a pilaster strip is handled by <em>IfcProjectionElement</em>
</blockquote>

<blockquote class="note"> 
NOTE&nbsp; View definitions or implementer agreements may restrict the types of elements to which <em>IfcProjectionElement</em> can be applied.
</blockquote>

<p>An <em>IfcProjectionElement</em> has to be linked to a element (all subtypes of <em>IfcElement</em>) by using the <em>IfcRelProjectsElement</em> relationship. Its existence depends on the existence of the master element. The relationship implies a Boolean union operation between the volume of the projection element and the volume of the element.</p>

<p>The <em>IfcProjectionElement</em> shall not participate in the containment relationship, i.e. it is not linked directly to the spatial structure of the project. It has a mandatory <em>ProjectsElements</em> inverse relationship pointing to the <em>IfcElement</em> that is contained in the spatial structure.</p>
<ul>
<li>The inverse relationship <em>ContainedInStructure</em> shall be NIL.</li>
</ul>

<blockquote class="history">
HISTORY&nbsp; New entity in IFC2x2.
</blockquote>

<blockquote class="change-ifc2x4">
IFC4 CHANGE&nbsp; The attribute <em>PredefinedType</em> has been added at the end of attribute list.
</blockquote>
